1. Field of the Invention
The invention relates to an electric hotplate and more particularly to a bushing or passage member therefor and to a method for fitting the same.
2. Prior Art
Bushings are conventionally used with standard electric hotplates with the hotplate body made from a cast material and are described e.g. in applicant's U.S. patent application Ser. No. 930,491 filed Nov. 12, 1986. These bushings have an all-round shoulder, by which they are pressed by the cover plate against the underside of the embedding material enclosing the heating means. They are consequently in thermal contact with the heating means and heat up relatively rapidly.
In addition, bushings are known, which are only held by the wires passing through them and are not directly supported on the embedding material. However, in order to ensure a reliable hold, they require another base located outside the cover plate (British Pat. No. 1 577 367).
Fitting must take place in such a way that the bushings are threaded manually onto the leads and must be moved into position before the cover plate is placed over the bushing and then fixed. However, such fitting is complicated and cannot be automated.
An object of the invention is to provide an electric hotplate with a bushing which, in the case of comparable electrical and mechanical safety and strength, permits an easier and optionally automatic fitting. This object is achieved according to the invention as disclosed and claimed.
The bushing can now be fixed initially to the cover plate which can then, together with the bushing, be engaged on the ends of the leads, which are normally made from solid wire. Preferably the bushing is a relatively flat, plate-like member, which is fitted to the cover by means of bent down retaining clips and has a significant spacing from the underside of the heating means. As a result the bushing has a relatively low thermal mass.
It has hitherto been assumed that the connecting piece should always have a direct thermal contact with the underside of the heating means, so as to permit rapid heating and avoid condensation of moisture on the bushing during the heating up phase and so that there is no inadmissible reduction in electrical safety (leakage currents). It has been found that this does not occur in the case of the invention, which is clearly due to the flat shape with a relatively large surface facing the heating means as compared with the thermal mass.
According to a preferred method, automatic fitting is possible, in that the leads, following the fixing of the bushing to the cover plate, are automatically gripped and aligned by a gripper, so that the bushing, together with the cover plate can be threaded over the same.
Further advantages and features of the invention are explained in the claims and the following description in conjunction with the drawings, individual features leading to advantageous constructions, both individually or in combination.